1. Technical Field
This invention relates to an apparatus and method for testing load bearing capacity on a pile or group of piles. In one aspect, this invention relates to novel apparatus and method for testing load bearing capacity on a pile or group of piles, utilizing a reaction anchor apparatus and method.
2. Background
In the construction industry, various types and shapes of piles are utilized for constructing foundations on the piles. These foundations are the structural supports upon which many types of constructions are built. Foundations support the loads imposed upon them and, hence, the loads imposed upon the piles, by such constructions as high rise buildings, power plants, river dams, and many other constructions.
Among the most common types and shapes of piles are timber piles, steel pipe piles, H-Piles, L-Piles, precast concrete piles, and cast-in-place concrete piles. These piles are in-stalled vertically or battered at an angle.
Piles are forced deep down into the soil by repetitive blows on their tops. These powerful blows are provided by pile-driving machines, also known as hydraulic hammers. Piles also can be poured-in, i.e., cast-in-place, by drilling a deep hole in the soil, then filling it with concrete. Generally, reinforcement steel rods, also known as rebar, are introduced into the hole prior to filling it with concrete.
The most commonly used method of installation of piles is by beating them down into the ground by means of a pile-driving machine.
Through the years, the construction industry has developed apparatus and testing methods for determining the capability of a vertical pile, a batter pile, or a group of piles to resist a required level of static compression loads as actually applied on the pile or group of piles. These testing methods determine whether a pile or group of piles has adequate bearing capacity or not.
Testing methods have been standardized by the American Society for testing materials, also known as ASTM. The Standard Test Method For Piles Under Static Axial Compressive Load, designation D1143-81, (reapproved 1987) covers pile testing utilizing conventional apparatus and methods for determining the capability of piles to resist a static compression load as actually applied on the piles.
According to ASTM D1143-81, single piles must be tested to 200% of the anticipated design load, while pile groups must be tested to 150% of the group design load.
Conventionally, for testing an individual pile, two additional piles have to be installed, using the same method and equipment utilized for installing the pile under test. These additional piles are driven into the soil on two diametrically opposing sides of the pile to be tested and at not less than seven feet from the pile being tested. These additional piles are known in the trade as anchor piles.
A test beam then is installed across the tops of the anchor piles, tying them to the beam and above the pile under test, forming what is known in the trade as a reaction frame. This test beam is set on a hydraulic jack, which in turn is set on top of the pile under test.
Upward hydraulic push is applied by the jack against the beam. The beam cannot move up because it is tied onto the anchor piles. As a result, the hydraulic power, i.e., the force exerted by the hydraulic jack, is applied downwardly against the top of the pile under test. These forces are applied incrementally, increasing at pre-established time intervals and held then at the maximum predetermined test loading for a specified length of time.
Certain instrumentation is utilized for determining the axial loading and for determining any movements, e.g., axial, rotational, and lateral, of the pile under test.
If the test proves the capability of the pile to resist the specified axially applied compressive loading, and if there are no other deviations beyond acceptable standards, then that pile is determined to be fit to be used for its intended purposes, i.e., it has adequate bearing capacity.
Testing a group of piles instead of a single pile utilizes the same procedure, but in the case of a group of piles, the various piles in the group are capped by a common cap, and the test load is applied uniformly upon the pile cap. Pile caps generally are poured, reinforced concrete slabs, specifically engineered for that purpose. A larger number of anchor pile pairs is required when testing pile groups.
After the test, anchor piles are left in place, after sawing off their tops, i.e., after sawing-off the top portion of the pile protruding above ground. It is extremely difficult and expensive to pull those anchor piles out of the ground.
Utilizing anchor piles for testing an installed pile or a group of piles presents several drawbacks.
One drawback of the conventional pile testing apparatus and methods is the large installation cost of driving into the soil one, two, or more pairs of anchor piles per each single pile or group of piles to be tested.
Another drawback of the conventional pile testings is the difficulty in handling the long and heavy anchor piles required for the testings, e.g., requiring a tractor and a trailer for their transportation, requiring a special crane for lifting in or out of the trailer, requiring an expensive, cumbersome pile driving machine for driving the anchor piles into the ground.
Another drawback of the conventional pile testings is the difficulty of setting the long and heavy anchor piles in a vertical position for driving them into the ground.
Yet another drawback of the conventional pile testings is the loss of the anchor piles, because after the test is completed, they are not reusable in future tests, and therefore, their top ends protruding above the ground have to be sawed off, abandoning the pile in the ground.
It is an object of the present invention to provide anchoring apparatus and installation methods which substantially reduce the cost of testing piles or group of piles.
Another object of the present invention is to provide anchoring apparatus and methods which simplify the pile testing process.
Yet another object of the present invention is to provide anchoring apparatus and methods for the testing of piles which simplify transportation and eliminate utilizing a tractor and a trailer.
Still another object of the present invention is to provide anchoring apparatus and methods for the testing of piles which do not require the use of a pile driving machine.
Another object of the present invention is to provide anchoring apparatus and methods for the testing of piles which do not require the use of anchor piles for the pile testing process.
Yet another object of the present invention is to provide anchoring apparatus and methods for the testing of piles which are reusable.
These and other objects of the present invention will become apparent from a careful review of the detailed description and the figures of the drawings, which follow.
The apparatus and method of the present invention provide novel means and method for testing piles for load bearing capacity. The novel means and method of the present invention include applying a static compressive force on a pile or group of piles to be tested for load bearing capacity, receiving an equal and opposite reaction force on an I-beam, providing at least two reaction anchor assemblies on opposite sides of the pile, and bracing the I-beam by the two reaction anchor assemblies to hold the I-beam stationary in counter-action against the opposite reaction force on the I-beam. In one aspect, each reaction anchor assembly has an anchoring head, a pipe column, a center, a pulling rod passing through the center, a pair of swingable anchoring plates and preferably two pairs of swingable anchoring plates, and a frusto-cone for pivoting the swingable anchoring plates. In one aspect, the pipe column has four fins welded longitudinally along the pipe column. In one aspect, the reaction anchor assembly is preassembled for transportation to a pile test site. The novel means and method for testing piles provide for retrieving the reaction anchor assemblies from the ground after completion of the pile test and reusing the reaction anchor assemblies from one pile test site to another.